[Bug gdb/26876] gdb error: internal-error: Unknown CFA rule when debugging the linux kernel with qemu

["robert at robertbuhren dot de" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26876

--- Comment #4 from robert at robertbuhren dot de ---
Hi, 
thanks for looking into this. I forgot to include my qemu setup, sorry for
that. There is no need to use any kind of guest OS to trigger the bug:

qemu-system-x86_64 -enable-kvm -m 4096 -smp 1 -kernel
linux/arch/x86/boot/bzImage -append "console=ttyS0 nokaslr" -S -s -nographic
-monitor tcp::4444,server,nowait -serial stdio

I let the kernel boot (it will panic because there is no /init to execute) and
then simply stop it via "CTRL-C": 

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(gdb) file vmlinux
Reading symbols from vmlinux...
(gdb) tar rem :1234
Remote debugging using :1234
0x000000000000fff0 in exception_stacks ()
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0xffffffff814222e0 in rdtsc_ordered ()
    at ./arch/x86/include/asm/msr.h:234
234             asm volatile(ALTERNATIVE_2("rdtsc",
(gdb) lx-symbols 
loading vmlinux
../../gdb/dwarf2/frame.c:1085: internal-error: Unknown CFA rule.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) y
This is a bug, please report it.  For instructions, see:
<https://www.gnu.org/software/gdb/bugs/>.

../../gdb/dwarf2/frame.c:1085: internal-error: Unknown CFA rule.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Create a core file of GDB? (y or n) y
fish: “gdb” terminated by signal SIGABRT (Abort)

Regards,
Robert

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